Electron discharge apparatus



w. T. GIBSON 2,317,140

ELECTRON DISCHARGE APPARATUS Filed Dec. '16, 1941 gm;lymmmmmlll l flINVEN TOR w T 0 135cm HTFOPN E Y Patented Apr. 20, 1943 ELECTRONDISCHARGE. APPARATUS William Thomas Gibson, London, England, assigner toInternational Standard Electric Corporation, New York, N Y.

4 Claims. (CL 250-27) This invention relates to electron dischargeapparatus foroperation at high frequencies and particularly to apparatusutilising the principles of velocity modulation of electron beams and ofthe excitation of high frequency resonators by the passage of electronsin pulses or bunches.

In one aspect the invention is concerned with electron dischargeapparatus wherein an electron beam modulated by the field of oneresonator is utilised to excite a second resonator and consists infeeding back high frequency energy from the second resonator to thefirst resonator by means of an auxiliary electron beam.

In another aspect the invention resides in electron discharge apparatuscomprising a pair of hollow resonators having aligned apertures, meansfor directing an electron beam through said apertures, so that the beamis velocity modulated in traversing the first resonator, and is bunchedon arrival at the second resonator and adapted to yield energy theretoand means for setting up an auxiliary electron beam and directing itthrough the second resonator and then through the first resonator tofeed back energy to the first resonator.

Preferably means are provided for varying the density and mean velocityof the auxiliary beam to permit adjustment of the amplitude and phase ofthe feedback.

The invention will now be described in more detail with reference to theaccompanying drawing, Fig. 1 of which is a diagrammatic representationof a known device for efiecting velocity modulation of an electron beam;whilst Fig. 2 shows an electron discharge apparatus according to oneembodiment of the present invention.

One known means of generating large amounts of power at very highfrequencies is by use of the device known as a Klystron. By high frequencies is meant frequencies of the order of 300 megacycles and above.

In this device a beam of electrons is fired successively through twohollow resonators tuned to the same frequency. A diagrammatic drawing ofsuch a device is shown in Fig. 1 of the accompanying drawing. In thisfigure, l represents a source of electrons, which may be an indirectlyheated oxide coated cathode. 2 is a focussing cylinder, whichco-operating with the cylinder 3 adjusted to appropriate voltagesproduces a beam of electrons which passes through the central tube andfinally arrives at a collecting anode 8. Electrodes 3 and 8 aremaintained at appropriate high potentials, and 2 may be at a negative,zero, or slightly positive potential with respect to the cathode. t and5 represent hollow resonators formed by revolution about the axis of thefigure, and should be made of a very good electrical conductor with veryclean inner surface.

At 6 and 1 are two sets of grids separated by small gaps. These gridsshould present as small an area for the collection of electrons aspossible. If an oscillation is assumed to exist in resonator a thenelectrons in the beam will be alternately accelerated and decelerated inpassing through the grid gap at 6. During the flight through the tube tothe next set of grids l, the accelerated electrons will advance withrespect to the decelerated electrons and by appropriate 1 adjustment ofthe velocity of the electron stream,

conditions can be found such that the electron stream arrives at gridgap I substantially in dense bunches separated by intervals whenrelatively few electrons arrive. If the bunches arrive at such momentsthat the field across the grids due to the local oscillation tends todecelerate them, then the electrons will do work on the system, withresulting amplification of the oscillation in resonator 8.

If a coupling represented by 9 is used to feed back oscillations toresonator t then by appropriate adjustment conditions can be found wherethe oscillations will rapidly build up to very high amplitude. It ispossible to extract power for useful purposes by a second coupling coilIll in the resonator 5 which feeds power via a concentric line formed byl and tube 2 to an antenna or other absorber.

In operating a device of this type, the adjustment of the coupling 9 isan important matter, and it is necessary to adjust it to the correctmagnitude for best results. Furthermore, there is a delay in the flightof electrons from 6 to I which may amount to several cycles. It isnecessary, therefore, to ensure that the phase lag in the coupling 9 isadjusted so that the phase lag between the two resonators suits thedistance 6 to I and the time of flight of the electrons.

With mechanical systems as shown it is difficult to secure thesevariations without complicated mechanical motions which must usually beoperated under high vacuum.

An alternative system to facilitate adjustment and control of feedbackcoupling is now proposed and will be particularly described withreference to Fig. 2 of the drawing.

In Fig. 2, dashed numerals apply to parts whose disposition and functionis unchanged from Fig. 1. In addition is shown another cathode In! andshield I02 sending a beam of electrons through a separate and relativelysmall diameter tube ofi'set in the resonators. The beam passes throughgrid gaps at I03 and I and through drift tube I04. The current requiredin this beam is very small compared with that in the main beam and theleft-hand grid at I05 may actually be a disc at which the electrons arecollected.

The performance of this beam is identical with that of the main beam,and its object is to transfer very small amounts of power back fromresonator 5' to resonator 4'.

The amplitude of the feedback is controlled by variation of the densityof the electron beam, for example by variation of potential of shieldI02 or by variation of the temperature and total emission of cathode IN.

The phase delay between resonator 5' and 4 can be compensated for byadjustment of the velocity of the electrons in the tube I04, which isdone by variation of the potential between the whole resonator systemand the cathode It".

In general, the voltage developed in resonator 5' will be very large andonly a small voltage is required to modulate the feedback beam. This isaccomplished by the offsetting of the electron beam from the centralposition.

It will be appreciated that the resonators may take various differentshapes and that various dispositions of the several parts particularlythe auxiliary beam system are possible. For example, the use offlattened resonators of an axial length comparable with the lengths ofthe gaps I03, I05 may simplify the construction. The auxiliary beam maybe inclined to the axis so that the couplings between the resonators andthe auxiliary beam are not equal. For example,

if the gap I05 is brought closer to the axis of the resonators, thebunched auxiliary beam will tend to set up a larger voltage in resonator4'.

What is claimed is:

1. Electron discharge apparatus comprising first and second hollowresonators having two sets of aligned apertures, means for producing amain electron beam, means for directing said main electron beam throughone set of aligned apertures in the direction from said first resonatorto said second resonator so that the said beam is velocity modulated intraversing said first resonator and is bunched on arrival at said secondresonator and yields energy thereto, and means for producing anauxiliary electron beam and for directing it through the other set ofaligned apertures in the direction from said secand resonator to saidfirst resonator whereby said auxiliary electron beam is velocitymodulated and feeds back energy from said second resonator to said firstresonator.

2. Electron discharge apparatus according to claim 6 wherein saidaligned apertures through which said main beam is directed are disposedalong the center line of the said resonators and the aligned aperturesthrough which said auxiliary beam is directed are disposed along a lineoff-set but parallel to said center line.

3. Electron discharge apparatus comprising first and second hollowresonators having two sets of aligned apertures, means for producing amain electron beam, means for directing said main electron beam throughone set of aligned apertures in the direction from said first resonatorto said second resonator so that the said beam is velocity modulated intraversing said first resonator and is bunched on arrival at said secondresonator and yields energy thereto, a cathode for producing anauxiliary electron beam for directing it through the other set ofaligned apertures in the direction from said second resonator to saidfirst resonator whereby said auxiliary electron beam is velocitymodulated and feeds back energy from said second resonator to said firstresonator, means for applying a positive potential to said resonatorsrelative to said cathode and means for varying the potential differencebetween said resonators and said cathode for varying the phase of theenergy fed back.

4. Electron discharge apparatus comprising first and second hollowresonators having two sets of aligned apertures, means for producing amain electron beam, means for directing said main electron beam throughone set of aligned apertures in the direction from said first resonatorto said second resonator so that the said beam is velocity modulated intraversing said first resonator and is bunched on arrival at said secondresonator and yields energy thereto, a cathode for producing anauxiliary electron beam, a focusing electrode for directing saidauxiliary electron beam through the other set of aligned apertures inthe direction from said second resonator to said first resonator wherebysaid auxiliary electron beam is velocity modulated and feeds back energyfrom said second resonator to said first resonator, means for creating apotential difference between said focusing electrode and said cathode,and means for varying said potential difference for varying theamplitude of the energy fed back.

WILLIAM THOMAS GIBSON.

